<COLGROUP ...> defines a group of columns in the table and allows you to set properties of those columns. <COLGROUP ...> goes immediately after the <TABLE ...> tag and before any
<TR ...>, <THEAD ...>, <TBODY ...>, or
<TFOOT ...> tags. <COLGROUP ...> works very much like <COL ...>, but be sure to note that <COLGROUP ...> requires both an opening and closing tag.
<COLGROUP ...> is most useful for defining column groups to use in conjunction with
<TABLE RULES=GROUPS> to put
borders between groups of columns instead of between every column. For example the following code creates a table that puts the first column in a group by itself, all the remaining columns in a group together, and puts borders between the groups of columns.